As photonics developed since 1980s, the concept of full photonics-based radar has been proposed and attracted wide attention from relevant research at home and abroad. Photonics possesses the advantages of large bandwidth, low loss, and low jitter, with application thereof being capable of breaking the “electronic bottleneck” existing in the traditional microwave/millimeter-wave radar systems, thus furnishing a new technical channel for generation, reception, and processing of a higher frequency and larger bandwidth wideband signal. Directed at the requirement for the carrier frequency and agility by a radar system, a full photonics-based coherent radar system has been realized. See, A full photonics-based coherent radar system, P. Ghelfi et al., Nature, vol. 507, no. 7492, pp. 341-345, 2014. Radar signal generation and reception in the system both come from the same mode-locked laser, thus insuring high coherence of the system, effectively inhibiting jitter of phase noise, and increasing radar detection accuracy. The system proves to have higher quantitative fidelity and detection accuracy in a validating demonstration with a 40 GHZ narrow band radar. Due to the excellent property of the system, the research by P. Ghelfi et al. has the potential to become a norm for designing the next generation radar system. See, Technology: Photonics illuminates the future of radar, J. McKinney, Nature, 2014, vol. 507, no. 7492, pp. 310-312, March 2014.
A radar system, like those in other wireless techniques, may only properly work under pre-designed bandwidths. A multiband radar may simultaneously or in a cross gating manner works in multiple bands, and thus has a higher probability over a common radar to detect a target. Due to the multiple frequency components contained in a signal transmitted by a multiband wideband radar, it is capable of breaking the wave-absorbing effect of narrowband frequency absorption materials, thus effectively increasing the anti stealth detection capability thereof. A multiband radar is further advantageous in inhibiting and dodging enemy ejected interference, which is crucial in increasing detection capability, in decreasing multipath loss and in strengthening self survival rate. See, Multiband Radar [C], Proceedings of The Fifteenth Annual Meeting of the Professional Radar Information Network of the Ministry of Industry and Information Technology, Su Bingrong, He Bingfa.
In actual applications, a microwave/millimeter-wave radar generally employs the following signal waveforms: short pulse signal, phase-coded signal, or chirp signal. Transmission and receiving techniques are very hard to implement for a short pulse signal, due to the extremely stringent requirement for the pulses thereof in high precision ranging, i.e., the requirement for an extremely narrow pulse width. A phase-coded signal is realized by loading phase information onto a continuous carrier wave according to defined time intervals, albeit has a comparatively high precision and sidelobe suppression ratio, is not suitable for a wideband system, due to the difficult implementation and its susceptibility to Doppler effect and limitation by its own dynamic range. In contrast, a chirp signal is widely employed in high precision ranging and radar detection, with ranging accuracy dependent on its modulated bandwidth, and is an ideal choice for a microwave/millimeter-wave radar.